In the heat lamination of light gauge plastic film to a heavier gauge substrate, it has been standard practice to employ a machine which consists basically of a framework in which two laminating rolls are mounted one above the other. The lower roll is rotatably mounted in the frame and will not move either vertically or horizontally with downward pressure as applied to it by the upper roll, which upper roll is vertically adjustable to lower the same to laminating position. The lower roll conventionally comprises a metal core covered with a layer of a resilient material, such as rubber or compounds having similar properties. The lower roll provides the surface against which lamination takes place when the upper roll is dropped under pressure on top of the two materials fed therebetween for lamination.
The upper roll is conventionally made of steel with a high polish and is mounted in the frame of the machine in a manner which permits it to be raised or lowered vertically by air or hydraulic pressure.
The heat necessary to produce lamination or fusion of the two materials is normally provided by the upper roll which is heated either internally or externally to the desired temperature. As the material passes between the rolls, heat is transferred from the surface of the upper roll through the light gauge plastic film into the substrate at the pinchpoint where the rolls meet, and this heats the two materials to a point where they fuse together. The surface temperature of the top of the upper roll is maintained by temperature-sensing units which feed additional heat to the upper roll as the surface temperature drops.
In the use of this type of equipment, it has been impossible up to the present time to prevent the formation of longitudinal ripples in the finished product after it leaves the laminating rolls. The presence of these ripples creates an unsatisfactory product which is not commercially acceptable for many uses, thereby resulting in serious losses in time and money to the manufacturer.